1. Field of Invention
This invention pertains to a reciprocating linear machine for conversion of electromagnetic energy into reciprocating motion of a member and vice versa by utilizing a coil having length which is independent of the stroke of the member.
2. Description of the Prior Art
Linear electromagnetic machines are known which comprise a stator having a plurality of axially spaced coils for generating magnetic circuits and a plunger reciprocating within the stator. Typical examples of such machines are found in U.S. Pat. Nos. 4,349,757 to S. K. Bhate and 4,454,426 to Benson.
However, an important limitation of the prior art configuration was that the coils were limited axially to the length of the plunger stroke. Therefore the number of turns and/or the size of the coil wire was similarly limited thereby limiting the total amount of power per slot that could be transferred by the machine. Accordingly, for a high power machine multiple coils were required causing the axial length of the machine to be integer multiples of the basic building block.
A further disadvantage of the prior art linear electromagnetic machines, and more particularly the machines used as motors was that in the absence of an excitation current, the plunger was urged by the magnetic field of the permanent magnet of the system towards one of the extreme ends of its travel. In other words, in prior art configurations in the absence of excitation currents, a magnetic force urged the plunger toward one or the other extreme ends of travel as stable points. This disadvantage of the prior art is overcome in the present invention by the provision of magnet rings which protrude beyond the magnetic circuit formed by the inner and outer stators. This arrangement results in a force on the plunger in the absence of current in the coil, to place the plunger symmetrically with respect to the stators. Thus, if the plunger is displaced from this symmetrical position, a centering force is exerted on the plunger to bring it back to the central position.